The present invention relates to arrangements for dimming gas discharge lamps with inductive ballasts.
The predominant trend in gas discharge (xe2x80x9cfluorescentxe2x80x9d) lighting is generally towards the use of electronic ballasts, which provide numerous advantages including the capability of effective dimming of the light. Nevertheless, due to the much higher cost of electronic ballasts for fluorescent lighting, inductive (or xe2x80x9cmagneticxe2x80x9d) ballasts are still widely used.
There is therefore a need for an effective and energy efficient arrangement for dimming a fluorescent light without requiring modification of the lamp or inductive ballast.
The present invention is an arrangement for dimming gas discharge lamps with inductive ballasts.
According to the teachings of the present invention there is provided, a dimmer arrangement for a gas discharge lamp assembly, the gas discharge lamp assembly including a gas discharge lamp and an inductive ballast, the dimmer arrangement being for connection to a domestic AC power supply, the dimmer arrangement comprising: (a) a first controllable switch deployed in series with the lamp assembly so as to selectively close a circuit from the power supply through the lamp assembly; (b) a second controllable switch deployed in parallel with the gas discharge lamp assembly so as to selectively close a circuit including the gas discharge lamp and the inductive ballast; (c) a controller operatively interconnected with the first and second controllable switches and configured to cyclically: (i) close the first controllable switch and open the second controllable switch, and (ii) close the second controllable switch and open the first controllable switch; and (d) a non-linear saturating inductance connected serially with the first and second controllable switches.
According to a further feature of the present invention, the controller closes and opens the switches at a frequency of at least 1 KHz.
According to a further feature of the present invention, the controller closes and opens the switches at a frequency of no more than 100 KHz.
According to a further feature of the present invention, the controller has an input indicative of a required degree of dimming, the controller being responsive to the input to vary a proportion of each cycle for which the first controllable switch is closed.
According to a further feature of the present invention, the controller is operative to close and open the first and second controllable switches such that a time of overlap during which both the first and second controllable switches are closed lies within a range of 1 nanosecond to 1 microsecond.
According to a further feature of the present invention, the non-linear saturating inductance has a soft magnetic core of cross-sectional area no greater than one square centimeter.
According to a further feature of the present invention, the non-linear saturating inductance includes a coil having no more than 10 turns.
According to a further feature of the present invention, the controller is an analogue controller.
According to a further feature of the present invention, the controller includes a digital processor.
According to a further feature of the present invention, the first and second controllable switches are implemented as transistors.
According to a further feature of the present invention, the first and second controllable switches are implemented as photo-transistors.